Casting two metals, cold and hot.

[GinZaikuShi]

I've been experimenting with casting lately, seeing what sorts of alloys, shapes, and colors I can make with what is laying around my shop.  Yesterday I did an experiment.  I filled a wood mold with cut up silver scraps, and poured molten copper into the mold.  What I got was an ingot of two distinct colors, swirled, with what seems to be a near perfect diffusion (I've been old and hot working the piece and haven't had any separation between the layers).

 

This first piece was cast in a bowl shaped mold and is mostly silver on one side and mostly copper on the other, with the swirlin where they meet.  I tried to give the resulting ingot a twist, to give it some more contrast on its faces.  I believe my next cast will be in a recangular mold, with the scrap silver laid out in lines or some sort of pattern.  I'm hoping that the pattern of the silver laid out in the mold will be somewhat preserved in the finished ingot.

 

Does anyone have any experience with this sort of casting?  I tried doing a few google searches on the subject and came up with nothing.  Maybe my phrasing wasn't quite right.  If anyone has any suggestions on creating better patterns, I'm all ears.

 

 

[Nobody Special]

Incas supposedly cast an alloy of platinum and gold by grinding up platinum to a near powder and casting gold around it or sintering the two together. I've had other metals embedded in castings before, but never on purpose. Sounds fun.

[SimonW]

Post some pictures please, your castings sound really interesting!

[ThomasPowers]

That's not sintering and for more information on that particular instance look up "depletion guilding".

 

About 30 years ago I was talking with a metallurgist at the University of Arkansas who was casting steel around cast iron spheroids and investigating carbon migration in the resultant. Dr Schwestra (sp???)

[Chinobi]

There's not much online about that particular process Gin. That or iv also been using the wrong keywords. When you lay out your wires or sheet or scrap or whatever cold metal you use try putting a lot of twists and curves in them so they will naturally occupy more volume. Straight pieces will tend to settle out at the bottom which will give you a wide disparity in distribution from top to bottom.

Do you think the swirling you mention is because the silver is melting into the copper before the ingot cools, or is it a function of the shape of the silver bits you started with?

Also, pics! I really want to see what you turned out here :)

[GinZaikuShi]

Pictures.  The first three are a piece that I cut from the larger ingot, squared and polished.  In the 4th picture, you can see the raw ingot.  They've been pickled for a few hours.  As you can see, there's a nice contrast between the two metals, but not much of a pattern.  I'm going to try and modify the process to produce a cast mokume gane.

 

The piece is really small.  I didn't want to waste any materials on an experiment that might not have worked.  I think all together this is about 10 g of silver and 30 g of copper.

 

 

 

 

[Chinobi]

If you want to get a densely patterned product like Mokume you could try using a larger number of smaller pieces of the cold metal. Maybe take some shears and just snip off a bunch of relatively small curls, or wrap some wire around a rod and make some jump rings. That way you won't have such large blocks of each metal showing.

Are you looking to have the ingot patterned like Mokume right out of the mold, or still work it after casting to develop the pattern?

[GinZaikuShi]

Having something similar to mokume out of the mold would be really cool and cut down on forging time.  I'm still expecting to have to work the pattern in somewhat, though.  I'm going to take that larger raw billet and square it up and see how many twists I can get in it.  I think if I got a lot of nice, tight twists, it would look pretty much like I went though the reular mokume process.

[Chinobi]

That should be pretty interesting to see :) I'm not sure it will be quite the same because with Mokume the layers go all the way through to produce the lines and stars. With the metals in bits and pieces I think it would give a somewhat interrupted twist. Impossible to say what it will look like though, I say go for it :-D

You using sterling, fine or coin silver btw?

[GinZaikuShi]

This billet was with 925 sterling scraps, cut up into about quarter inch squares.  I picked up a nice lot of silver coins though, and i'll be melting down all the junk rosy dimes for my next batch (Don't worry, I checked for rare dates and kept them).  I'm going to try for a billet with Shibuichi and 900 silver scraps, and maybe a sprinkle of brass shavings from my grinder.  I wish I had a bit of gold or shakudo shavings to throw in.

[Chinobi]

Yer off the edge of the map man :) if that turns out it should be pretty awesome! How are you going to add the brass? Just dusted onto the scrap in the mold or sprinkles in while you pour (might require a third hand) or something else?

[GinZaikuShi]

I'm thinking sprinkles in the mold, before adding the silver and shibuichi.  The hope would be that the piece would be patterned copper, silver, sibuichi, with a random speckling of brass.

 

I saw this Mokume bracelet the other day while browsing Google Images.  I really like it.  It doesn't really have a pattern, but I think a look like this could easily be produced the way i've been talking about.  I think it could serve to have more colors, personally, and I like something a little more fluid than hectic.

 

http://jerrycblanchard.wordpress.com/2012/05/01/contemporarymokumebracelet/

[Frosty]

NO BRASS!!!! Brass and silver make silver solder, the eutectics make for a really low melting temperature!

 

This looks like a lot of fun to mess with and I'm not a jewelry kind of guy. Drill type shavings, narrow twisty, curly strips and scrunched up wire might make for some cool patterns.

 

To get a more "traditional" mokume pattern I'd lay strip of sheet silver that fit the mold with equal thickness spaces and pour the copper between.

 

Maybe stand silver wire kind of close on end and fill from the end.

 

Frosty The Lucky.

[GinZaikuShi]

Would the brass really have that sort of effect?  I'm not making an alloy, I'm kind of forge weld cheating.  The copper and the silver didn't combine, I'm not sure if the brass would.  Even if the brass did alloy with the silver, wouldn't it only be in small spots (assuming i'm using a lot of silver scrap and a small amount of brass scrap)?

[Chinobi]

I didn't think it would be that much of a problem, but the potential does exist for it to occur.  brass and silver melting points are both below that of copper, and the eutectic bonding point that creates the silver solder problem is significantly below that (something like 600C IIRC). so it is entirely possible that you might end up with little bubbles of silver solder that develop in your billet and could expand when annealed or overheated working it.  these could also squirt out if they occur near edges and are hammered while the silver solder is still liquid, which would be less than great :)

 

that bracelet is pretty cool though, its a ladder pattern (nominally) though fairly distorted.  I like the engraving on the silver backing too, makes it look as if it was stitched on like leather :)

 

as to dusting the mold with your sprinkles before anything else, im not sure if the turbulence of the pour will be sufficient to really distribute that very well, you might just end up with some dusty voids in the bottom or corners where the brass bunched up and prevented the copper from flowing.

 

if you have some bronze that might be a better route to take for the gold highlights.

 

it feels like you are taking pages right out of my sketchbook, so keep the test reports coming!  I really appreciate you sharing with us as there is really very little info out there in this direction =/ (and feel free to tell me to stuff it if I am living too vicariously through your experiments :P)

[ThomasPowers]

Note that you can dissolve copper wire in molten Al that is *MUCH* lower temp than the melting point of copper.

[Chinobi]

very interesting, I did not know that Thomas!

 

Gin:

this has been the closest/only thing I have been able to find in my research of mixed metal casting, though I was looking at hot/hot rather than hot/cold at the time.  I dunno where this will fall in terms of outside linking so ill just say google up 'Miles of Alaska jewelry' and check out the 'cast metals art' link on the left to see some of his work casting copper/brass and copper/silver into the same mold.

[GinZaikuShi]

Not a great day for casting today.  Broke through my crucible today.  made another with what was laying around.  Did two big ingots probably 4-5 Toz each.  Problem:  I think I got the copper too hot in the forge.  The ingots don't really have a pattern.  I think the silver might have just incorporated into the copper, and I just made an alloy.  I have really bad eyesight though, so I'll find out when they come out of the pickle.

[GinZaikuShi]

My friend did get this awesome picture of me pouring though.

 

[Chinobi]

neat pic indeed!

 

sorry to hear about your crucible, out of curiosity what was it made of and what are you making your replacement from?  I know next to squat about DIY crucibles except that I'm not inclined to risk it :)

 

far be it from me to point it out (way guilty of it myself) but I know somebody is going to chime in with recommendations to upgrade your PPE.  I would at least move casting from the top of your anvil to a baking pan filled with dry sand, that way a mis-pour wont seize your channel locks or get all over your anvil.  to say nothing of condensation and the like :)

 

those are indeed some pretty hefty ingots you are pouring, and especially if you suspect your copper was running too hot you may well have alloyed in crucible as the elevated temperature and greatly increased thermal mass of the larger pour might have been enough to bring the silver up to its melting point before the whole thing solidified.  if that's the case I hope you got some cool waves or distribution patterns, like swirling dye through water, which would be really neat to see!

 

what all did you end up loading your ingot molds with prior to pouring anyway?

[GinZaikuShi]

I've actually gone through 2 crucibles so far.  The first one was a section of a titanium alloy bike stem that I cut off and stuffed a bunch of red mud and refractory clay in the bottom of.  It lasted about three pours.  On the third pour, the shaft was so brittle that it crumbled in the tongs.

 

The second crucible was a piece of steel pipe tack welded to a piece of steel plate, again with the bottom filled with mud and clay.  It lasted 2-3 weeks, a few dozen pours.  The problem is that the steel scales away in the forge and the walls of the crucible get thinner and thinner.  I'm sure there is also some cross contamination from the oxidizing steel.

 

This third one is pretty much an improvement on the 2nd.  Thicker steel pipe, thicker plate.  Welded the seam all the way around, then on the inside, then a bigger weld on the outside a second time on top of the first weld.  It's bigger than the second and holding up nicely.  Was able to fill it with about 40 copper pennies and some scrap copper sheet.

 

As for PPE, I do need to figure out a better place to do my casting, and build a purpose built foundry for the process.  I pour into big wooden molds that are painted with wet blasting clay and let to dry next to the opening of the forge until they're a bit charred.  I've had no problem even pouring into a wet wooden mold.  I've been sprayed with molten silver a few times when attempting to make silver mokume.  It cools down fast and just stings a little. haha.

 

I've got a look at my ingots, and they're just big chunks of Shibuichi.  I'll end up using them, but I'm still disappointed.  There seems to be a key temperature for doing the pour.  The copper needs to be hot enough to melt the silver and bond the silver to the copper, but the copper must cool before the silver can be incorporated into an alloy.  I think this just means smaller, faster pours.  To try and get a big ingot, I filled the crucible with copper and let it melt and filled it more, like three times.  It was way too hot and in the forge too long.  The crucible was yellow, I usually pour when the crucible matches the orange of the forge.  And then it's still a bit cooler, since I usually give it a stir before pouring.  I guess if I'm going to try and pour that much copper, I need to let it cool a bit after coming out of the forge.  Or I can just do one heat and make small billets.

 

I also wonder what would happen if I poured some very hot silver over copper scraps.

 

I just filled my mold with 925 silver scraps and some shibuichi scraps.

[Chinobi]

I think you need to strike a balance between the hot mass and the cold mass such that your copper doesn't transfer so much heat to the silver that it melts and that there isn't so much cold silver that it chills the copper prematurely. If you were really bent on it you could probably do the math if you look up the thermal properties of copper and silver.

Are you just visually inspecting your ingots or have you cut into them yet? It would be neat to see how much diffusion you actually got. That might help you eyeball just how much the balance of temp and material needs to be adjusted. If the silver has been completely dispersed you are way way too hot/too much copper, vs clear bond failure or oxide inclusions showing perhaps too much silver/not enough heat. Clean metals will also help provide a better surface for the metals to bond, kinda like Mokume.

Using a lower melting point metal as the hot component may provide a safety net against alloying the whole thing accidentally, but as Mr Powers shared earlier it's not foolproof. I am curious though if that can happen in the time it would take the aluminum to chill or if that's done stirring the aluminum melt with copper while it's still being actively heated and at a stable liquid temperature.

[GinZaikuShi]

I melted copper pennies into molten aluminum in a little paint can foundry once.  It took forever, stirring with the AL at a constant temp.

 

With pouring silver onto copper, I'd be more afraid that the copper wouldn't get hot enough to bond or swirl into the metal.  Maybe I could preheat the copper or something.  Do you think I should be using flux when doing this?

 

I haven't cut into my ingots, but they don't at all look like the first two I poured.

 

Know anyting about silver plating?  I got a box of bold flat nails.  I want to silver plate them and make them into rings.  I need some more colored metals to play around with.

 

I got a job today, so I don't think I'll be able to do much casting the next few days.  Lame.

[ThomasPowers]

copper plate them and then silver plate the copper  (and probably make the ring first and then plate it!)

[Chinobi]

id say having a job is better than not having a job :) though i do miss the plethora of free time =/

 

iv been having the same debate about preheating and flux with myself for a while but i havent tested anything yet.  my feeling is that the flux could potentially get stuck under a layer or just not migrate to the surface before the metal freezes which will leave voids and flux inclusions in the finished product.  if you preheat try to keep it from getting hot enough to for visible oxide patinas on the surface, that would start to impede the metals from bonding.  at least thats my theory :)

 

with hot silver/cold copper i doubt there will be much if any actual diffusion of copper into the silver unless you poured the silver really hot, you could try using really thin shavings or thin curly drill shavings that will get hot very quickly and even if they dont actually diffuse their shape would be kinda wavy =/

 

iv never plated with silver so i would defer to Powers on that one, there are probably solutions or sets available online for such projects.  check out the work that John B posted in this thread, some really cool projects from horse shoe nails that he had chrome plated afterwards. '?do=embed' frameborder='0' data-embedContent>>

 

get ahold of or make yourself some bronze to add another 'gold' hue to your inventory that will play more nicely with the silver.